This invention relates to a toroidal type continuously variable transmission which is enabled, by clamping rolling members between input rotary members and output rotary members opposed to each other, to transmit a torque between the individual rotary members through the rolling members and which is enabled to vary the gear ratio continuously by inclining the rolling members to vary the radii of the torque transmitting positions of the rolling members relative to the individual rotary members and, more particularly, to a toroidal type continuously variable transmission including a plurality of sets of speed change units composed of the aforementioned individual rotary members and rolling members.
The transmission of the torque in the toroidal type continuously variable transmission of this kind occurs at contact portions through an oil film among an input disc corresponding to the input rotary member, an output disc corresponding to the output rotary member and disc-shaped power rollers clamped between those input and output discs and corresponding to rolling members. If the contact pressure between the discs and the power rollers is raised within a range of no breakage of the oil film, the torque to be transmitted increases. If the contact pressure between the discs and the power rollers is raised, however, the torque transmission efficiency drops, and a disadvantage is involved in the durability of the continuously variable transmission.
In order to eliminate this inconvenience, there has been developed in the prior art the so-called xe2x80x9cdouble cavity type toroidal continuously variable transmissionxe2x80x9d, which uses a plurality of sets of toroidal speed change units arranged in parallel and each composed of input/output discs and power rollers sandwiched between those discs to suppress the torque of each toroidal speed change unit and to increase the torque capacity. The continuously variable transmission of this kind has a single input element such as an input shaft and a single output element such as an output shaft. It is, therefore, preferable that the gear ratios to be set at the individual toroidal speed change units (i.e., the individual cavities) are always equal. When the clamping forces for clamping the power rollers are to be varied by the individual discs or when the gear ratios are to be varied, however, the gear ratios in the individual cavities may be different to cause slips between the individual discs and the power rollers.
With the slips between the individual discs and the power rollers, the oil film can break to cause the direct contacts between the discs and the power rollers. In the inventions disclosed in Japanese Patent Laid-Opens Nos. 6-174034 and 8-233054, therefore, the construction is made to cause the differential rotations between the individual output discs and the output shaft. Specifically, the continuously variable transmission, as disclosed in those Laid-Opens, is the so-called xe2x80x9cdouble cavity type toroidal type continuously variable transmissionxe2x80x9d, in which the output discs are arranged, so to speak, in a xe2x80x9cback-to-back relationxe2x80x9d, in which input discs are arranged across and opposed to those output discs with clamping those discs and in which the power rollers are individually sandwiched between the output discs and the input discs. In the former continuously variable transmission disclosed in Japanese Patent Laid-Open No. 6-174034, moreover, the individual output discs and the output shaft are coupled through a differential mechanism. In the latter continuously variable transmission disclosed in Japanese Patent Laid-Open No. 8-233054, on the other hand, the individual output discs and the output shaft are coupled through a viscous coupling (or a viscous clutch).
The differential mechanism, as disclosed in the aforementioned Japanese Patent Laid-Open No. 6-174034, is a double pinion type planetary gear mechanism or the mechanism in which a pair of side gears are held by a differential carrier and connected to the individual output discs and in which the differential carrier is connected to the output shaft. On the other hand, the viscous clutch, as disclosed in the Japanese Patent Laid-Open No. 8-233054, is a clutch in which a viscous fluid is confined between a plurality of input discs and output discs so that differential rotations occur between those discs to transmit the torque. This clutch is arranged on the common axis between the output discs in the continuously variable transmission.
In either of the continuously variable transmissions disclosed in the Laid-Opens, therefore, the differential gear mechanism or the viscous coupling is interposed between the output discs which are arranged in the so-called back-to-back relation. Therefore, the number of components to be arranged on the common axis is increased to enlarge the entire length. A disadvantage of worse mountability is caused when the continuously variable transmission is employed as the speed change device for a vehicle.
This invention has been conceived noting the aforementioned technical problem and has an object to provide a toroidal type continuously variable transmission which can shorten the entire length.
In order to achieve the aforementioned object, this invention is characterized by giving a function to absorbing a difference between individual cavities (or toroidal speed change units), to either a transmission mechanism for transmitting a motive power to a continuously variable transmission or a transmission mechanism for outputting the motive power from the continuously variable transmission. According to this invention, more specifically, there is provided a toroidal type continuously variable transmission, which has a plurality of sets of such speed change units of its power transmitting rolling members are interposed between the opposed faces of input rotary members and output rotary members as inclined to vary the torque transmitting portions to those faces and; in which the input rotary members at individual speed change units are coupled to a single input member whereas the individual output rotary members are coupled to a single output member. Said input rotary members or said output rotary members are held rotatably relative to each other, and the individual input rotary members are coupled in a torque transmitting manner to said input member through the individual wrapping transmission mechanisms, or the individual output rotary members are coupled in a torque transmitting manner to said output member through the individual wrapping transmission mechanisms.
The continuously variable transmission of this invention is provided with a plurality of sets of the so-called xe2x80x9cspeed change unitsxe2x80x9d in which the rolling members are clamped between the input rotary member and the output rotary member, and the torque is inputted from the input member to the individual input rotary members and is outputted from the individual output rotary members to the output member. The input rotary members can rotate relative to each other, and the torque is transmitted to those input rotary members through the wrapping transmission mechanism. Alternatively, the output rotary members can rotate relative to each other, and the torque is transmitted from those output rotary members through the wrapping transmission mechanism. Between the input rotary members and the output rotary members, the rolling members transmit the torque, and the rolling members are inclined to vary the radii of the torque transmitting positions relative to the individual rotary members so that the gear ratio is continuously varied.
The gear ratios at the individual speed change units are basically set equal, but the gear ratios to be set at the individual speed change units may be transitory different. In this case, the input rotary members or the output rotary members can rotate relative to each other, and these relative rotations are allowed by the backlash or chattering in the wrapping transmission mechanism. Therefore, there is allowed the difference in the gear ratio and the speed due to the fact that the angles of inclination of the individual rolling members are transitory different. As a result, even if the gear ratios are transitory different at the individual speed change units, no slip occurs between the individual rotary members and the rolling members. Moreover, the input or output transmission mechanism acts as the mechanism for allowing the relative rotations, as described hereinbefore. Therefore, the number of components such as components arranged in series on the axial direction can be reduced to shorten the entire length of the continuously variable transmission.